Depressive illnesses, as epidemiological studies have consistently shown, are amongthe most frequent psychicdisorders encountered in hospital and everyday practice. Moreover, during the last few decades the prevalence of depression has definitely been increas- ing. Its alarming frequency - especially among women - has re- cently been confirmed once again by epidemiologicalfindings pub- lished in the United States of America. The World Health Organi- zation estimates the world-wide prevalence of depression at 3% to 5%. Amongthefactors contributingtothecurrentincreaseareexces- sively abrupt changes in social structures and living conditions, as well as a departure from traditional values which is often accompa- nied by disruptionofthe family unit and loss ofreligious faith. Fur- ther factors include the unfettered materialism ofthe modern age, the hectic pace of technological progress, and the loneliness to which elderly people in particular are exposed. Finally, the increas- ing life expectancy ofthe population in almost all countries ofthe world raises the incidence of cardiovascular disorders, brain dis- ease, and malignanttumors,thusinevitably addingtothe riskofde- pressive illness in old age. The prominent position occupied by the diagnosis and treat- ment of depression in everyday medical practice is apparent from the results ofan enquiry conducted among some 15000 doctors in Austria,the Federal RepublicofGermany, France, Italy, Spain,and Switzerland. This enquiry disclosed that ofall patients consulting a doctor,upto 10% - and sometimesmore - couldbeclassifiedas de- pressed, and that in more than one-halfofthe patients a so-called masked form ofdepression was found. Duringthe last 15years, biological psychiatricresearchfocusing on depression has made more significant progress than everbefore.